Systems For Erasing Non-Volatile Memory Using Individual Verification And Additional Erasing of Subsets of Memory Cells

Abstract

A set of non-volatile storage elements is divided into subsets for erasing in order to avoid over-erasing faster erasing storage elements. The entire set of elements is erased until a first subset of the set of elements is verified as erased. The first subset can include the faster erasing cells. Verifying the first subset includes excluding a second subset from verification. After the first subset is verified as erased, they are inhibited from erasing while the second subset is further erased. The set of elements is verified as erased when the second subset is verified as erased. Verifying that the set of elements is erased can include excluding the first subset from verification or verifying both the first and second subsets together. Different step sizes are used, depending on which subset is being erased and verified in order to more efficiently and accurately erase the set of elements.

Description

PRIORITY CLAIM[0001]This application is a continuation application of U.S. patent application Ser. No. 11 / 296,028, entitled, “SYSTEMS FOR ERASING NON-VOLATILE MEMORY USING INDIVIDUAL VERIFICATION AND ADDITIONAL ERASING OF SUBSETS OF MEMORY CELLS,” by Hemink, et al., filed Dec. 6, 2005, which claims priority from U.S. Provisional Patent Application No. 60 / 667,043, entitled “NON-VOLATILE MEMORY ERASE OPERATIONS WITH OVER-ERASE PROTECTION,” by Hemink et al., filed Mar. 31, 2005, both of which are incorporated by reference herein in their entirety.CROSS-REFERENCE TO RELATED APPLICATIONS[0002]The following applications are cross-referenced and incorporated by reference herein in their entirety:[0003]U.S. patent application Ser. No. 11 / 296,055 (Attorney Docket No. SAND-01066US0), entitled, “ERASING NON-VOLATILE MEMORY USING INDIVIDUAL VERIFICATION AND ADDITIONAL ERASING OF SUBSETS OF MEMORY CELLS,” by Hemink et al., filed on Dec. 6, 2005;[0004]U.S. patent application Ser. No. 11 / 295,747 (...

AI Technical Summary

Benefits of technology

[0022]A set of non-volatile storage elements (e.g., a NAND string) can be divided into subsets for erasing in order to avoid over-erasing faster erasing storage elements. The entire set of elements is erased until a first subset of the set of elements is verified as erased. The first subset can include the faster erasing elements. Verifying the first subset includes excluding a second subset from verification. After the first subset is verified as erased, they are inhibited from erasing while the second subset is further erased. The set of elements is verified as erased when the second subset is verified as erased. Verifying that the set of elements is erased can include excluding the first subset from verification or verifying both the first and second subsets together. Different step sizes can be used, depending on which subset is being erased and verified, in order to more efficiently and accurately erase the set of elements.

Problems solved by technology

This can lead to over-erasure of faster erasing memory cells because they will continue to be subjected to erase voltages that are applied to sufficiently erase the slower memory cells of the NAND string.

Thus, the different erase rates can result in a shorter cycling life of a memory cell or NAND string.

Soft programming, however, may increase program and erase times.

In addition, traditional soft programming can suffer from some of the same effects of disparate properties among different memory cells.

The same memory cells that may be slow to erase, may also be slow to soft-program.

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